The development of wireless local area networks ("WLAN") for computers has facilitated the use of portable devices such as laptop computers for network communication. Such computers are small by design and, thus, present space constraints for communication units associated with them. For example, laptop computers are provided with slots in which accessory cards can be inserted. These slots and the associated circuitry generally have a prescribed standard configuration such as the PCMCIA standard. A communication device used with such a computer must conform to this standard.
Typically, a PCMCIA card used for wireless communications has been fitted with a transceiver and an antenna for communication by the computer. However, these cards have not been completely effective because portable computers are often used in complex radio frequency ("RF") environments such as office buildings and the like, where WLAN's are usually installed. These environments include physical barriers which give rise to multiple reflections of the signals transmitted or received by the computer. The signals travel over multiple paths, resulting in interference patterns and thus "dead spots". The radio frequency environment is further complicated by movement of persons or equipment within the environment. Additionally, the portable computers will be moved from location to location, thus changing the radio frequency environments in which they are to be operated.
It has been proposed to address these problems by using a tethered antenna which can be moved by the user to a position where signal strength is sufficient. Such tethered designs, however, present an inconvenience in that the tether requires the user to continually set up the antenna when moving the portable device to a different location. They can also give rise to mechanical stress, and resulting failure, of the wires used in the tether.
Another proposed solution is the use of multiple antennas to provide spatial diversity, so that if one of the antennas is in a dead spot, the other one is likely to encounter a usable signal. However, spatial diversity has not provided sufficient immunity to fading and, thus, such solutions have not been effective.
There remains a need for a low cost, more reliable antenna assembly which conforms to the available space in a portable communication device, the antenna of which allows maximum signal propagation while experiencing minimal fading in a dynamic RF environment.